Tacker Error :alarm_receiver.py :Unauthorized

We have installed openstack with basic nova,neutron,glance,heat,horizon,keystone services from newton official tutorial . We have also installed tacker,ceilometer,aodh. We have created a scaling policy with tacker which should spawn a new VM when aodh alarm is captured (i.e certain event goes beyond threshold). However when alarm is triggered by Aodh , we get error at tacker server stating :

At alarm_receiver.py:44 An error occurred during processing the request :Request at ......
Unauthorised : The request you have made requires authentication.HTTP 401